Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The broken-line rectangle at the periphery of the FIGURE illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining broken lines show portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 